A known way to control filling in a filling machine is to use a probe. These probes typically extend into the container through its container opening during filling. Examples of such probes are electrical fill-level probes with at least one probe contact that, when dipped into the filling material level as it rises in the container during filling, triggers a probe signal. This probe signal serves as a basis for closing the liquid valve or triggering such closure with a delay, so that the particular target fill-level or target fill-depth in the container is reached.
Another kind of probe for determining the fill-depth uses gas-return pipes. These are used when the container is sealed against a filling machine. In this case, incoming filling material displaces the gas already in the container. This gas escapes through the gas-return pipes. Eventually, the liquid rises enough to submerge the opening to the gas-return pipes. At this point, gas can no longer escape. The resulting pressure buildup halts further entry of liquid.
In all known filling systems that use a gas-return pipe, the closing of the particular filler element or of the liquid valve occurs only after an interval of a varying duration and at a specified position or angular position of the movement of the rotating transporting element. This may occur long after the target fill depth has been reached. This delay results in some disadvantages.
One disadvantage is a risk that, in the time it takes to close the liquid valve after the liquid has reached the target fill level, a malfunction may cause over-filling of the container. These malfunctions can arise from many causes, such as pressure fluctuations, sudden changes in the speed of rotation of the transporting element, and/or by shaking. Moreover, there is frequently no way to avoid having the filling material rise well into the gas-return pipe or into its gas-return channel after the gas-return pipe has dipped into the filling material level of the filling material.
Another disadvantage is the need to empty the gas-return pipe into the relevant container at the end of the actual filling phase to prevent the dripping of the filling material when the filled container has been removed from the filler element. Waiting for this dripping to occur wastes time. And if one does not wait long enough, there is a risk that contamination in one container will spread to subsequently filled containers.
It is also known in the art to design the probes that determine the fill depth, such as electrical fill-level probes or gas-return pipe for setting the fill depth or the fill level, to be axially height-adjustable.